3 to 6 degrees of Knock Retard

[wagnerm672]

Hi all,

Brand new to tuning but have been on the Gen 3 and Gen 4 LS platform. Currently own a 2008 Pontiac G8 GT L76 with 77k miles on the odometer.
Had it taken to a shop in Toms River, NJ. Kept getting knock above 4800 RPM, tuner told me it was oil getting into the chamber. Added a catch can (yes it's hooked up correctly), replaced the valve stem seals, locks, springs as well and cleaned the intake and TB.

Took it back and car was still getting 6 to 8 degrees of knock retard and the tuner is stumped. Got a refund from him.

Car has OBX headers, LS7 Cam with DoD delete, stock heads, stock head gaskets, back to GXP mufflers, 3.27 gears, Cai.

Spoke to a buddy of mine and we adjusted the knock sensors 5% at a time, halved the attack, adjusted burst knock. I looked at the whole exhaust and I don't see a single thing rubbing the car or subframe.

Log I am uploading is another run I did today, still got 3-6 degrees of knock. Hoping you guys have any ideas what else I can quickly check or what else I can do. Car should be making another 30-40WHP.

Thanks in advance.

[5FDP]

What's your wideband saying for fuel ratio?

I see you are commanding around a 12.8 AFR, it's possible that it's too lean. You could try running it around 12.2-12.4 and see if the knock gets any better. Just throwing an idea out there.

[Niemer]

I do know these cars have really sensitive settings and seem to report a lot of false knock. See if your tuner has a sensor hooked up to headphones so he can listen to it when it is reporting knock, that way you'll know if it's real of not.

[gmorris]

Have you tried race gas or torco to see if octane reduces it...that would mean its real knock.

[reconscout]

Is there a way to log the voltage from the knock sensor? I have an 09 g8 gt and cant find it to log it. I've been logging the total knock retard and have pretty much the same thing going on as you. I'd like to follow this thread to see what helps.

[wagnerm672]

I remember removing the knock sensor to make it easier to install my starter. I may have it misaligned or over tightened. So I ordered 2 AC Delcos.

When I get back from vacation im trying race gas.

I don't have a wideband yet. Was relying on the tuner to get me going on current mods so I don't know what actual air to fuel is other than in that dyno log.

I'll command a lower air to fuel and see what it does on way home from airport then replace knock sensor and make sure it's aligned and try race gas as a last resort.

[schpenxel]

Put some torco and/or race gas in it

See if anything changes

Turn timing down maybe 5* and see if anything changes

If knock is still showing up on race fuel and less timing I'd have a hard time believing it's real unless you can actually hear it or something

[06MonteSS]

add more fuel at WOT.. 12.8 is too lean for those cars.. they like it a little richer.. 12.4/12.5... reduce timing a few degrees at WOT...

[wagnerm672]

@06MonteSS,

If you take a look at the AFR on the dyno log it is below 12.0 AFR even when there is 8 degrees of knock. Should the commanded afr still be 12.2 instead of 12.8?

[FASSTRUK]

Closest accuracy is to follow wot afr with a wideband, stay out of pe until you have one.

[wagnerm672]

So I loaded up with 3.5 gallons of E98, essentially race gas, and 15.5 gallons of 93 octane gas. Giving me abut 100 octane fuel. Went and made 3 pulls. Still getting knock. I will post the tune and my logs. But where in the **** is this knock coming from. The timing is more conservative than stock, is it definitely false knock?

[rbooth]

I doesn't look like you have accounted for the ethanol content. From my experience G8's like .85-.83 lambda. With you mixing fuels you basically have E26. Although you have raised the octane it appears that you are over a point on the lean side. Stoich for E26 is around 13.2 afr not 14.68. I see you are logging ethanol content but doesn't look like you have a sensor on it. If you want to use that blend I would change the stoich table to reflect and change your PE to 1.18 to 1.2 and see if that helps. Although not accurate for wot tuning your narrow bands indicate its on the lean side as well. You definitely need that wideband to verify.

[BigDaddyCool]

If your closed loop trims are anything to go by........... and my l76 cam only ran 16' at 12.5afr

[wagnerm672]

I was trying to use the ethanol as race gas to determine whether or not the knock was false or true knock. I do not have the sensor for it yet. I ran 12.56 AFR, 14.68/1.171 , and I had absolutely no knock. I am going to try and repeat a few runs with 93 gas and see what it gets me.

Also the logging for ethanol is because I copied a buddies layout to help with logging, it's just there. Again I am not setup for ethanol yet.

I will post the log and tune later but I was getting 21.5 degrees of spark no problem now.

[rbooth]

My point was with that much ethanol you should have been commanding a rich eq. Or modifying the stoich table. Anyway, glad you got the knock stopped.

[wagnerm672]

Just ran a full tank of 92 Octane gas. Knock came back. If I splash in some more fuel, around 12.2 AFR and retard the timing 2 degrees in each cell, it goes away. Would this be an indication of bad rings? Or what am I looking at? Shouldn't these cars run 12.5-12.9 all day with no knock?

Thanks in advance.

[FASSTRUK]

Your injector pulse is at 12.xx at wot during the logs with kr, seems kind of low.

[wagnerm672]

What should it be? Are you saying it may just be that the injectors aren't spraying enough fuel even though I am commanding plenty?

[FASSTRUK]

My 2008 tbss w/ tune for cai, metallic high flow cats and 3" cat back exhaust has an injector pulse of 20.0 at wot. My afr on the wideband is 12.2 with no knock. 93 octane NY gas. So yours should be higher if your injectors are stock.

[rbooth]

Did you install a wideband? Cylinder airmass seems a little low and as others have said so does the injector pw .